Liquid crystal display device and its driving method

ABSTRACT

A liquid crystal display device capable of displaying in multiple colors, and a method for driving the liquid crystal display device using a typical monochrome liquid crystal driving IC. A display portion of a birefringence color liquid crystal display device has a usual letter display portion ( 41 ) for displaying letters in a single color and a mark display portion ( 42 ) for displaying a variety of colors. A liquid crystal cell is driven by supplying scanning signals to scanning electrodes for the letter display portion ( 41 ) and data signals to scanning electrodes for the mark display portion ( 42 ).

TECHNICAL FIELD

This invention relates to a liquid crystal display device and itsdriving method, and, more particularly, to constitution of abirefringence color liquid crystal display device and a driving methodfor a liquid crystal cell thereof.

BACKGROUND TECHNOLOGY

Conventionally, liquid crystal display devices typically use areflection-type liquid crystal display device which displays inmonochrome employing a TN (twisted nematic) liquid crystal cell or anSTN (super twisted nematic) liquid crystal cell. Generally, atransflective reflector is utilized as a reflector of a liquid crystaldisplay device, and a backlight unit, such as an electro-luminescent(EL) light and a light emitting diode (LED) array, is provided outsidethe transflective reflector for visibility of the time display at night.

Recently, watches equipped with liquid crystal display device, portabletape recorders, cellular phones, portable game machines or the like arecoming into fashonable, so a liquid crystal display device capable ofcolorful displaying is desired for them. Then, for example, a digitaltimepiece capable of color displaying by using a single-color liquidcrystal display device which indicates white letters or the like on ablue or red background through a color polarizing film dyed with adichroic pigment, has been developed.

However, for developing a timepiece that is more fashionable in designand portable machines that have stronger impact in appearance, it is notenough to use a single-color display device. Then, it is desired toprovide a multi-color display device capable of displaying a pluralityof colors.

It is proposed to mount a birefringence color liquid crystal displaydevice in a timepiece or other portable machines to perform a multicolordisplay with the birefringence effect of liquid crystal by changing thevoltage applied to a liquid crystal cell instead of using a colorfilter.

In order to change colors on a letter (in case of a watch, numerals todisplay normal time, an alarm time and a calendar) display portion usingthe birefringence color liquid crystal display device, RMS voltage ofthe signal supplied to the letter display portion must be variable. Inorder to change the effective value, an IC for driving liquid crystalthat is capable of controlling gray scale is required, this results inan increase of development cost and an extension of the time period fordevelopment. Moreover, the complexity of driving circuits increases thesize of the driver IC and the amount of current consumed.

DISCLOSURE OF THE INVENTION

As regards a birefringence color liquid crystal display devicedisplaying in a multi-color, it is an object of the present invention toprovide a way to display in a multi-color easily in which thebirefringence color liquid crystal display cell is driven by a typicalmonochrome liquid crystal driving IC without a gray scale function forsimple multi-color display at a low cost and low power consumption.

To attain the aforementioned object, the present invention provides aconfiguration for a liquid crystal display device, consisting of: aliquid crystal cell in which nematic liquid crystal is sandwiched andfilled in a gap between a transparent first substrate, having firstelectrodes, and a transparent second substrate, having secondelectrodes; a pair of polarizing films respectively arranged on andunder the liquid crystal cell; and a reflector arranged on a face of oneof the polarizing films which is on the opposite side to the liquidcrystal cell.

The display portion made up of the liquid crystal display cell consistsof a letter display portion displaying in a single color and a markdisplay portion displaying in a plurality of colors.

A liquid crystal cell driving circuit for driving the liquid crystaldisplay device to supply scanning signals to the first electrodes forthe letter display portion, data signals to the first electrodes for themark display portion, and data signals to the second electrodes for boththe letter display portion and the mark display portion, is provided.

The reflector of the liquid crystal display device may be atransflective reflector. And a backlight unit for lighting the liquidcrystal elements through the transflective reflector may be preferablyprovided on the opposite side of the reflector to the liquid crystalcell.

A retardation film or a twisted retardation film may be provided betweenthe liquid crystal cell and the polarizing film positioned on thevisible side thereof in the liquid crystal display device.

The liquid crystal cell is preferably an STN liquid crystal cell inwhich the nematic liquid crystal is aligned at a twist angle in therange from 180° to 270°. Accordingly, a Δnd value which is the productof a value Δn in the birefringence of the liquid crystal and a gap d ofthe liquid crystal cell, preferably ranges from 1300 nm to 1600 nm.

In case of the above-mentioned liquid crystal display device having theretardation film, the liquid crystal cell is, preferably, an STN liquidcrystal cell in which the nematic liquid crystal is aligned at a twistangle in the range from 180° to 270°. Accordingly, a Δnd value which isthe product of a value Δn in the birefringence of the liquid crystal anda gap d of the liquid crystal cell, preferably ranges from 1500 nm to1800 nm, and a retardation value of the retardation film desirablyranges from 1600 nm to 1900 nm.

It is advisable that the retardation film forms relations of nx>nz>ny,where nx is the refractive index of the direction of a phase delay axis,ny is the refractive index in a direction orthogonal to the phase delayaxis, and nz is the refractive index in a thickness direction.

In the use of the liquid crystal display device mentioned above havingthe twisted retardation film, the liquid crystal cell is, preferably, anSTN liquid crystal cell in which the nematic liquid crystal is alignedat a twist angle in the range from 180° to 270°. Accordingly, a Δndvalue which is the product of a value Δn in the birefringence of theliquid crystal and a gap d of the liquid crystal cell, preferably rangesfrom 1500 nm to 1800 nm. A Δnd value of the twisted retardation filmpreferably ranges from 1400 nm to 1800 nm.

Another liquid crystal display device according to the present inventionhas: a first liquid crystal display device consisting of a first liquidcrystal cell in which nematic liquid crystal is sandwiched and filled ina gap between a transparent first substrate having first electrodes anda transparent second substrate having second electrodes, a pair ofpolarizing films respectively arranged on and under the first liquidcrystal cell, and a reflector arranged on a face of one of thepolarizing films which is on the opposite side to the liquid crystalcell;

a second liquid crystal display device, arranged on a face of the firstliquid crystal display device on the visible side, consisting of asecond liquid crystal cell in which nematic liquid crystal is sandwichedand filled in a gap between a transparent first substrate having firstelectrodes and a transparent second substrate having second electrodes,and a third polarizing film arranged on a face of the second liquidcrystal cell on the visible side; and

a liquid crystal cell driving circuit for driving the first and secondliquid crystal display devices to supply scanning signals to the firstelectrodes of the first liquid crystal cell, data signals to the secondelectrodes of the first liquid crystal cell, and data signals to thefirst electrodes and the second electrodes of the second crystal liquidcell.

It is advisable that the second liquid crystal display device has areflection-type polarizing film on the opposite side of the secondliquid crystal cell from the visible side.

A driving method of the liquid crystal display device according to thepresent invention is for a birefringence color liquid crystal displaydevice, as described hereinbefore, which consists of: a liquid crystalcell in which nematic liquid crystal is sandwiched and filled in a gapbetween a transparent first substrate having first electrodes and atransparent second substrate having second electrodes; a pair ofpolarizing films respectively arranged on and under the liquid crystalcell; and a reflector arranged on a face of one of the polarizing films,the face being on the opposite side to the liquid crystal cell, and inwhich a display portion thereof has a letter display portion displayingin a single color and a mark display portion displaying in a pluralityof colors.

According to the method, the aforementioned liquid crystal cell isdriven by supplying scanning signals to the first electrodes for theletter display portion; supplying data signals to the first electrodesfor the mark display portion; and supplying data signals to the secondelectrodes for both the letter display portion and the mark displayportion.

The present invention also provides a method for driving a liquidcrystal display device which comprises: a first liquid crystal displaydevice consisting of a first liquid crystal cell in which nematic liquidcrystal is sandwiched and filled in a gap between a transparent firstsubstrate having first electrodes and a transparent second substratehaving second electrodes, a pair of polarizing films respectivelyarranged on and under the first liquid crystal cell, and a reflectorarranged on a face of one of the polarizing films, the face being on theopposite side to the liquid crystal cell; and a second liquid crystaldisplay device arranged on the visible side of the first liquid crystaldisplay device and consisting of a second liquid crystal cell in whichnematic liquid crystal is sandwiched and filled in a gap between atransparent first substrate having a first electrode and a transparentsecond substrate having a second electrode, and a third polarizing filmarranged on a face of the second liquid crystal cell on the visibleside. According to the method, the first and second liquid crystal cellsare driven by supplying scanning signals to the first electrodes of thefirst liquid crystal cell while supplying data signals to the secondelectrodes thereof; and supplying data signals to the first electrodeand the second electrode of the second liquid crystal cell.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plane view showing a display portion of a liquid crystaldisplay device of a first embodiment according to the present invention,and

FIG. 2 is a sectional view showing an arrangement of the liquid crystaldisplay device;

FIGS. 3 and 4 are plane views showing the positional relations betweenthe liquid crystal cell and polarizing films in the liquid crystaldisplay device;

FIG. 5 is a chromaticity diagram showing display colors of the liquidcrystal display device;

FIG. 6 is a plane view showing a configuration of first electrodes on afirst substrate of the liquid crystal display device, and

FIG. 7 is a plane view showing a configuration of second electrodes on asecond substrate of the liquid crystal display device;

FIG. 8 is a waveform table of signals assigned to the respectivescanning electrodes shown in FIG. 6, and

FIG. 9 is a waveform table showing signals assigned to the respectivedata electrodes D1, D5, D9 and D10 shown in FIG. 7, and combinationwaveforms with the signals supplied to the scanning electrode C4;

FIG. 10 is a waveform table showing the combination waveform and thesignals supplied to the scanning electrodes and the data electrodes;

FIG. 11 is a plane view showing a display portion of a liquid crystaldisplay device of a second embodiment according to the presentinvention, and

FIG. 12 is a sectional view showing an arrangement of the liquid crystaldisplay device;

FIGS. 13 and 14 are plane views showing the positional relations betweenthe liquid crystal cell and polarizing films in the liquid crystaldisplay device;

FIG. 15 is a chromaticity diagram showing display colors of the liquidcrystal display device;

FIG. 16 is a plane view showing a configuration of first electrodes on afirst substrate of the liquid crystal display device, and

FIG. 17 is a plane view showing a configuration of second electrodes ona second substrate of the liquid crystal display device;

FIG. 18 is a waveform table of signals assigned to the respectivescanning electrodes shown in FIG. 16, and

FIG. 19 is a waveform table showing signals assigned to the respectivedata electrodes D1 to D5 shown in FIG. 17, and combination waveformswith the signals supplied to the scanning electrode C5;

FIG. 20 is a plane view showing a display portion of a liquid crystaldisplay device of a third embodiment according to the present invention,and

FIG. 21 is a sectional view showing an arrangement of the liquid crystaldisplay device; and

FIGS. 22 and 23 are plane views showing the positional relations betweenliquid crystal cells and polarizing films in the liquid crystal displaydevice.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments for carrying out the present invention will bedescribed hereinafter with references to the accompanying drawings.

First Embodiment: FIGS. 1 to 10

The first embodiment according to the present invention will be detailedwith references to FIG. 1 to FIG. 10.

Examples of display pattern on the display portion of a liquid crystaldisplay device of the first embodiment are described with reference tothe plane view of FIG. 1. The display portion of the liquid crystaldisplay device 17 consists of a letter display portion 41 displayingcurrent time and alarm time in digital form and mark display portions 42respectively formed above and under the time display portion 41, asshown in FIG. 1. The mark display portions 42 are each composed of aplurality of circular patterns 43 to 46 showing multiple colors forrepresenting a colorful display. The letter display portion 41 does notchange color, but always displays time in a predetermined color.

The mark display portions 42 display in different colors on therespective circular patterns, and the color is varied, for example, onceevery second. Colorfulness and amusement can be expressed by varying thecolor approximately every 0.1 seconds.

The sectional arrangement of the liquid crystal display device 17 isexplained with reference to FIG. 2.

As shown in FIG. 2, the liquid crystal display device 17 in theembodiment is composed of a liquid crystal cell 7; a first polarizingfilm 9 and a second polarizing film 8 which are laid under and on theliquid crystal cell 7 respectively; and a reflector 10 provided outsidethe first polarizing film 9.

Regarding the liquid crystal cell 7, a first substrate 1, which is madeof a glass plate with a thickness of 0.5 mm and on which transparentfirst electrodes 3 made of Indium Tin oxide (hereinafter “ITO”) aremounted, is fixed by a sealing member 5 to a second substrate 2, whichis made of a glass plate with a thickness of 0.5 mm and on whichtransparent second electrodes 4 made of ITO are mounted, the substrates1 and 2 having a certain spaced interval between. In this space, nematicliquid crystal 6, which is aligned at a twist angle of 220°, issandwiched and filled into the gap between the substrates 1 and 2.Resulting in the liquid crystal cell 7 in an STN mode.

The first polarizing film 9 and the reflector 10 are arranged outsidethe first substrate 1 of the liquid crystal cell 7 in the STN mode, andthe second polarizing film 8 is arranged outside the second substrate 2thereof, thus forming the birefringence color liquid crystal displaydevice 17 of a reflection type.

On the surfaces of the first electrodes 3 and the second electrodes 4,alignment layers (not shown) are respectively formed. As shown in FIG.3, the first substrate 1 undergoes a rubbing treatment upward to theright at a 20° angle with respect to a horizontal axis H, whereby alower molecular alignment direction 7 a of liquid crystal is disposedupward to the right (counterclockwise) at a 20° angle. The secondsubstrate 2 undergoes a rubbing treatment downward to the right at a 20°angle, whereby an upper molecular alignment direction 7 b is disposeddownward to the right (clockwise) at a 20° angle. A so-called “chiral”substance, which is an optical rotatory material, is added to thenematic liquid crystal. The nematic liquid crystal has a viscosity of 20cp. The chiral substance is added such that the twisting pitch P isadjusted to 14 μm, thus forming the STN mode liquid crystal cell 7twisted counterclockwise to a 220° angle.

A difference Δn in birefringence of the nematic liquid crystal 6 is setto be 0.21 and a cell gap d which is a gap between the first substrate 1and the second substrate 2 is set to be 7 μm. Accordingly, a Δnd valueof the liquid crystal cell 7 which is represented by the product of thedifference Δn in the birefringence of the nematic liquid crystal 6 andthe cell gap d, is 1470 nm.

As shown in FIG. 4, an absorption axis 8 a of the second polarizing film8 is directed downward right at a 60° angle with respect to thehorizontal axis H. An absorption axis 9 a of the first polarizing film9, as shown in FIG. 3, is directed upward right at a 75° angle withrespect to the horizontal axis H. Consequently, the pair of upper andlower polarizing films 8 and 9 forms an intersecting angle of 45degrees.

In the aforementioned liquid crystal display device 17 where no voltageis applied, a light linearly polarized in the direction vertical to theabsorption axis 8 a of the second polarizing film 8, is incident at an50° angle with respect to the upper molecular alignment direction 7 b ofthe liquid crystal cell 7, so as to assume an elliptic polarized state.By the elliptic polarized state and the optimization of the arrangementangle of the polarizing films 8 and 9, the light that has passed throughthe first polarizing film 9 changes to a bright pink color. This coloredlight is reflected by the reflector 10, and returns to pass through thefirst polarizing film 9, the liquid crystal cell 7 and the secondpolarizing 8, and then emitted to the visible side to create a pinkdisplay.

On the other hand, when a voltage is applied across the first electrodes3 and the second electrodes 4, molecules of the nematic liquid crystal 6rise, and the apparent Δnd value of liquid crystal cell 7 is reduced.Hence, the elliptic polarized state generated in the liquid crystal cell7 is changed, to vary colors.

FIG. 5 is a chromaticity diagram showing a color display of the liquidcrystal display device. A thick curved 20 with arrows indicates a changein color during a gradual increase in voltage applied across the firstelectrodes 3 and the second electrodes 4 in the liquid crystal cell 7,shown in FIG. 2, from a no-voltage state.

The initial color on the display is pink when no voltage is applied, butas the voltage is gradually increased, the color changes to light green,green and blue, and finally to white when applying a high voltage.

A configuration of electrodes in the liquid crystal cell 7 of the liquidcrystal display device 17 will be now explained with references to FIG.6 and FIG. 7.

FIG. 6 is a plane view from the top of the first electrodes 3, made ofITO and formed on the upper face of the first substrate 1. FIG. 7 is aplane view from the top of the second electrodes 4, made of ITO andformed on the lower face of the second substrate 2. In these drawings,electrode patterns are indicated and heavy lines indicateinterconnection patterns thereof. Incidentally, reference numeralsrespectively correspond to the time display portion 41 and the markdisplay portions 42 shown in FIG. 1 are indicated.

As shown in FIG. 6, the first electrodes 3 consist of five scanningelectrodes C1 to C5. The scanning electrodes C1 to C3 are connected torespective electrode patterns which form the letter display portion 41.The scanning electrode C4 and the scanning electrode C5 are connected toa plurality of circular electrodes which form the mark display portions42 to display in multiple colors.

In the drawing, the scanning electrodes C1 to C5 are extended to theleft side of the display screen for easy explanation. Practically, thescanning electrodes C1 to C5 are generally electrically connected to thesecond substrate 2 by a conductive paste or anisotropic conductivebeads.

As shown in FIG. 7, the second electrodes 4 consist of twenty dataelectrodes D1 to D20. Interconnection for the data electrodes haveseveral types such as: an interconnection to only the electrode patternfor the letter display portion 41, e.g. the data electrode D2; anotherinterconnection to only the circular electrode for the mark displayportion 42, e.g. the data electrode D10; and the other interconnectionto both electrodes for the time display portion 41 and the mark displayportion 42, e.g. the data electrode D1.

In the case of 1/3 duty multiplex drive, typically, the data electrodeis connected to all three pixels. However, the mark display portion 42has no bearing on an actual display, so that in the letter displayportion 41, it is sufficient that the data electrode is connected to anynumber of the three pixels.

A method for driving the liquid crystal display device will be explainedbelow with references to the driving signals shown in FIG. 8, FIG. 9 andFIG. 10. FIG. 8 shows signals supplied to the scanning electrodes C1 toC5 shown in FIG. 6. FIG. 9 shows signals supplied to the data electrodesD1, D5, D9 and D10 among the data electrodes shown in FIG. 7, andcombination waveforms supplied to the liquid crystal between thescanning electrode C4 for the mark display portion 42 and the dataelectrodes. FIG. 10 shows signals supplied to the scanning electrodesand the data electrodes in the liquid crystal display device, andexamples of the combination waveforms actually supplied to the liquidcrystal in the case of the 1/3 duty multiplex drive, a half bias and adrive voltage of 3V.

To the scanning electrodes C1 to C3 for the letter display portion 41,the normal scanning signals as shown in FIG. 8 are supplied. To thescanning electrodes C4 and C5 for the mark display portion 42, the datasignals are supplied. Now, a data signal of ON/ON/ON is supplied to thescanning electrode C4, and a data signal of OFF/OFF/OFF is supplied tothe scanning electrode C5.

Hence, as shown in FIG. 9, to the pixel connected to the scanningelectrode C4, a voltage is applied in four strengths of voltage,V3=3.0V, V2=2.45V, V1=1.73V and V0=0V, as combination waveforms due tothe data signals assigned to the data electrodes D1, D5, D9 and D10. Thevoltage has an effective value, in which V3 becomes the square root of(3²+3²+3²)/3 is 3, V2 becomes the square root of (3²+3²+0²)/3 is 2.45,and V1 becomes the square root of (3²+0²+0²)/3 is 1.73. Other voltagesshown below are also effective values.

As shown in the top boxes in FIG. 9, an OFF/OFF/OFF data signal issupplied to the data electrode D1. Hence, the pixel (segment) of theletter display portion 41 connected to the data electrode D1 hasVoff=1.22V, so that the display color is the same pink as the backgroundcolor. The combination waveform with the signal for the scanningelectrode C4 has V3=3V, so that the circular pattern 43 in the markdisplay portion 42 shown in FIG. 1 displays a white color (the colordisplayed with the maximum applied voltage as shown in FIG. 5).

As shown in the second box in FIG. 9, an OFF/OFF/ON data signal issupplied to the data electrode D5. Hence, the pixel of the letterdisplay portion 41 connected to the data electrode D5 has Voff=1.22V, sothat the display color is pink same as the background color. Thecombination waveform with the signal for the scanning electrode C4 hasV2=2.45V, so that the color of the circular pattern 44 in the markdisplay portion 42 shown in FIG. 1 is blue (the color displayed when theapplied voltage is slightly lower than the maximum thereof in FIG. 5).

In the third box in FIG. 9, an OFF/ON/ON data signal is supplied to thedata electrode D9. Hence, the pixel of the letter display 41 connectedto the data electrode D9 has Voff=1.22V and Von=2.12V, so that therespective display colors are pink and green which are the same as thebackground color. The combination waveform with the signal for thescanning electrode C4 has V1=1.73V, so that the display color of thecircular pattern 45 in the mark display portion 42 shown in FIG. 1 islight green (the color displayed when the applied voltage is slightlyhigher than the minimum thereof in FIG. 5)

In the bottom box in FIG. 9, an ON/ON/ON data signal is supplied to thedata electrode D10. The pixel of the letter display portion 41 is notconnected to the data electrode 10, so that the display colors in thetime display portion 41 are insensitive to the applied voltage on thedata electrode D10. The combination waveform with the signal for thescanning electrode C4 has V0=0V, so that the display color of the pixel46 in the mark display portion 42 shown in FIG. 1 is the same pink asthe background color (the color displayed when the applied voltage isminimum in FIG. 5).

FIG. 10 shows a relation between the signal waveform supplied to thescanning electrode and the data electrode, and the combination waveformactually supplied to liquid crystal molecules.

A scanning signal used for a typical multiplex drive is supplied to thescanning electrode for the time display portion 41. Examples of thewaveform in the case of a 1/3 duty multiplex drive, a half bias and adrive voltage of 3V, are shown in the drawing.

A scanning signal is composed of a select period Ts for applyingvoltages of 0V and 3V, and an unselect period Tns for applying a voltageof 1.5V, with one frame being formed by the select period Ts and theunselect period Tns. When an ON signal is sent from the data electrodeto the select period Ts, ignoring an ON signal or an OFF signal of thedata signal assigned to the unselect period Tns, the combinationwaveform assumes a fixed effective value Von. On the other hand, when anOFF signal is sent from the data electrode to the select period Ts,ignoring the data signal assigned to the unselect period Tns, thecombination waveform assumes an effective value Voff, thus achieving adesired letter display.

Meanwhile, to the scanning electrodes C4 and C5 for the mark displayportion 42 shown in FIG. 1, the same data signal as that fundamentallyreceived by the data electrode is supplied. Examples when an ON/ON/ONdata signal is supplied to the scanning electrode are shown in thebottom box in FIG. 10. When a data signal is supplied to the scanningelectrode, the combination waveform in the 1/3 duty multiplex driveassumes four types of effective value due to the data signal supplied tothe data electrode.

When a data signal supplied to the data electrode is ON/ON/ON, the datasignal and a data signal supplied to the scanning electrode are negatedmutually, so that a voltage applied to the liquid crystal becomes V0=0V.When a data signal supplied to the data electrode is ON/ON/OFF,two-thirds of the periods in a frame carry a voltage of 0V, andone-third of the periods in a frame carry a voltage of 3V, so that thecombination waveform assumes an effective value of V1=1.73V. When a datasignal supplied to the data electrode is ON/OFF/ON or OFF/ON/ON, aneffective value is identical to the effective value of V1.

Similarly, when a data signal supplied to the data electrode isON/OFF/OFF, one-third of the periods in a frame carry a voltage of 0Vand two-thirds of the periods carry a voltage of 3V, so that thecombination waveform assumes an effective value of V2=2.45V. When a datasignal supplied to the data electrode is OFF/OFF/ON or OFF/ON/OFF, aneffective value is identical to the effective value of V2.

When a data signal supplied to the data electrode is OFF/OFF/OFF, thecombination waveform assumes an effective value of V3=3V.

As described hereinbefore, a value of a voltage applied to the liquidcrystal is permitted to vary in value to V0, V1, V2 and V3.Consequently, in the watch which installs the birefringence color liquidcrystal display device capable of varying colors with a change in theapplied voltage, the display color of the mark display portion 42 can bechanged by supplying the data signal to the scanning electrode for themark display portion 42 even when a typical monochrome liquid crystaldriving IC without a gray scale function is employed therein.

In other words, the embodiment allows the time display portion 41 todisplay green letters on a pink background, and the circular patterns43, 44, 45 and 46 as each pixel in the mark display portion 42 todisplay in multiple colors such as white/blue/light green/pink. Since amonochrome liquid crystal driving IC has a simple circuit, a small sizeand low power consumption compared with those of a color liquid crystaldriving IC, the use of monochrome liquid crystal driving IC ispreferable, giving longer battery life in a timepiece or portablemachines.

The data signals, supplied to the data electrodes, are changed atintervals of from approximately 0.1 seconds to one second, whereby thedisplay color of each circular pattern in the mark display portion 42 inturn is changed at intervals of 0.1 seconds to one second, thus allowinga colorful and impressive display screen, resulting in the provision ofnovel portable machines for young people.

Modification of the First Embodiment

The liquid crystal display device used in the watch of the firstembodiment employs the STN mode liquid crystal cell 7, having a Δndvalue=1470 nm at a twist angle of 220°, as a liquid crystal cell.However, a color display similar to that of the first embodiment can beobtained insofar as a Δnd value ranges from 1300 nm to 1600 nm.

When a Δnd value of the liquid crystal cell 7 is smaller than 1300 nm,the amount of the change in an apparent Δnd value through theapplication of a voltage decreases, thus colors of blue and white arenot easily displayed. On the other hand, when the Δnd value exceeds 1600nm, a pink color on the background is not easily displayed.Consequently, any Δnd value of less than 1300 nm and more than 1600 nmis undesirable.

In either using a TN mode liquid crystal cell or an STN mode liquidcrystal cell having a twist angle of more than 180°, the birefringencecolor liquid crystal display device similar to that described in theembodiment, but differing in the color tone therefrom, can be obtained,hence providing a colorful watch.

The liquid crystal display device for a watch is described in theembodiment but, as a matter of course, the present invention isadaptable to liquid crystal display devices for a portable taperecorder, a cellular phone or the like.

The first embodiment describes the first electrodes 3 as the scanningelectrodes and the second electrodes 4 as the data electrodes, butreversibly, the second electrodes 4 may operate as the scanningelectrodes and the first electrodes 3 may operate as the dataelectrodes. In this case, the scanning signals are assigned to thesecond electrodes 4 for the time display portion 41 and the data signalsare assigned to the second electrodes 4 for the mark display portions42.

Second Embodiment: FIGS. 11 to 19

A second embodiment according to the present invention will be describedwith references to FIGS. 11 to 19.

A color liquid crystal display device in the second embodiment differsfrom that of the first embodiment in the points of: the provision of aretardation film and a pattern of an electrode; a driving signal for theliquid crystal display device; and the provision of a backlight unit.The remaining structure of the liquid crystal display device in thesecond embodiment is the same as that in the first embodiment.

As shown in FIG. 11, the display portion of the liquid crystal displaydevice 18 is made up of a letter display portion 51 in a dot matrixdisplay for displaying current time and alarm time, and mark displayportions 52 which are respectively formed above and under the timedisplay portion 41 and display a variety of colors. Each mark displayportions 52 consist of a plurality of circular patterns 53, 55 and 57and square patterns 54 and 56. The time display portion 51 does notchange color, and always displays time in a predetermined color.

The mark display portions 52 display in different colors on therespective patterns 53 to 57, and the color is varied once every second.The color is varied approximately every 0.1 seconds, thus achievingcolorful and impressive portable machines, a watch or the like.

FIG. 12 shows the sectional arrangement of the liquid crystal displaydevice, in which the same reference numerals will be used to designatecomponents corresponding to those in the liquid crystal display deviceof the first embodiment shown in FIG. 2 and the description thereof willbe omitted.

In a liquid crystal cell 12 of the liquid crystal display device 18, anematic liquid crystal 6, which is aligned at a twist angle of 240°, issandwiched and filled into a gap between the first substrate 1 and thesecond substrate 2, to form an STN mode liquid crystal cell.

Outside the second substrate 2 of the liquid crystal cell 12, the secondpolarizing film 8 is arranged to sandwich the retardation film 13 with aretardation value of 1800 nm therebetween. Outside the first substrate1, the first polarizing film 9, a transflective reflector 11 and abacklight unit are arranged. Because transflective reflector 11 partlytransmits a light from underneath, the backlight unit 19 can illuminatethe liquid crystal cell 12 through the transflective reflector 11 bybeing positioned under the transflective reflector 11. Therefore, atransflective type birefringence color liquid crystal display device 18can be formed.

Alignment layers (not shown) are respectively formed on the surfaces ofthe first electrodes 3 and the second electrodes 4 of the liquid crystalcell 12. The first substrate 1 undergoes a rubbing treatment upward tothe right at a 30° angle with respect to a horizontal axis H shown inFIG. 13, whereby a lower molecular alignment direction 12 a of liquidcrystal is disposed upward to the right at a 30° angle. The secondsubstrate 2 undergoes a rubbing treatment downward to the right at a 30°angle, whereby an upper molecular alignment direction 12 b of liquidcrystal is disposed downward to the right at a 30° angle. The nematicliquid crystal has a viscosity of 20 cp. A so-called “chiral” substance,which is an optical rotatory material, is added to the nematic liquidcrystal. The chiral substance is added such that the twisting pitch P isadjusted to 16 μm, thus forming the STN mode liquid crystal cell 12twisted counterclockwise at 240° angle.

A difference Δn in birefringence of the nematic liquid crystal 6 used isset to be 0.21 and a cell gap d which is a gap between the firstsubstrate 1 and the second substrate 2 is set to be 8 μm. Accordingly, aΔnd value of the liquid crystal cell 12 which is represented by theproduct of the difference Δn in the birefringence of the nematic liquidcrystal 6 and the cell gap d, is 1680 nm. The retardation value for theretardation film 13 is set to be a value 120 nm larger than the Δndvalue of the liquid crystal cell 12.

A uniaxial stretching film made of a polycarbonate film is used for theretardation film 13. Accordingly, the equation nx>ny=nz is obtained,where nx is a refractive index of a phase delay axis 13 a of theretardation film, ny is a refractive index in a y-axis directionorthogonal to the phase delay axis 13 a, and nz is a refractive index ina z-axis direction as a thickness direction.

As shown in FIG. 14, the retardation film 13 is arranged to dispose itsphase delay axis 13 a upward to the right at a 65° angle with respect tothe horizontal axis H. The absorption axis 8 a of the second polarizingfilm 8 is disposed counterclockwise at a 45° angle with respect to thephase delay axis 13 a of the retardation film 13. As shown in FIG. 13,the absorption axis 9 a of the first polarizing film 9 is disposedcounterclockwise at a 35° angle with respect to the lower molecularalignment direction 12 a of the liquid crystal cell 12. The pair ofupper and lower polarizing films 8 and 9 form an intersecting angle of45°.

As for the aforementioned birefringence color liquid crystal displaydevice 18, in a no-voltage state, a linearly polarized light incidentfrom the second polarizing film 8 assumes an elliptic polarized state bythe birefringence effect of the retardation film 13. Thereafter, theelliptic polarized light returns to a linearly polarized light whenpassing through the liquid crystal cell 12 due to a difference betweenthe retardation value of the retardation film 13 and the Δnd value ofthe liquid crystal cell 12, and the optimized arrangement-angle of thepolarizing films. In this time, when the positional relation between theabsorption axis 9 a of the first polarizing film 9 and the absorptionaxis 8 a of the second polarizing film 8 forms an intersecting angle of45° as described in the embodiment, the linearly polarized light doesnot pass through the first polarizing film 9, so that the display colorbecomes black.

On the other hand, when a voltage is applied across the first electrodes3 and the second electrodes 4 of the liquid crystal cell 12, moleculesof the nematic liquid crystal 6 rise, and the apparent Δnd value ofliquid crystal cell 12 is reduced. For this reason, the ellipticpolarized light generated in the retardation film 13 does not return toa complete linearly polarized light even after passing through theliquid crystal cell 12. Consequently, the light in the ellipticpolarized state reaches the first polarizing film 9, and a light havinga certain wavelength passes through the first polarizing film 9,resulting in a colored light. The colored light after being passedthrough the first polarizing film 9 is reflected by the transflectivereflector 11, and it returns to pass through the first polarizing film9, the liquid crystal cell 12, the retardation film 13 and the secondpolarizing film 8 in order, and then it is emitted towards the visibleside to display in color.

FIG. 15 is a chromaticity diagram showing a color display of thebirefringence color liquid crystal display device 18. A thick curvedline 21 with arrows indicates a change in color with a gradual increaseof the applied voltage from a state of no applied voltage. In ano-voltage state, the display color is approximately black. While avoltage is applied gradually to increase, after the display colorchanges to white once, it then changes to yellow, red, blue, green, andfinally to light green when the voltage is further applied.

A configuration of electrodes in the liquid crystal display device 18 of10 the second embodiment will be now explained with references to FIG.16 and FIG. 17. FIG. 16 is a plane view from the top of the firstelectrodes 3, made of ITO and mounted on the upper face of the firstsubstrate 1 of the liquid crystal cell 12. FIG. 17 is a plane view fromthe top of the second electrodes 4, made of ITO and mounted on the lowerface of the second substrate 2.

As shown in FIG. 16, the first electrodes 3 of the liquid crystal cell12 in the liquid crystal display device 18 consist of six scanningelectrodes C1 to C6. The scanning electrodes C1 to C4 are respectivelyconnected to four transverse bar-shaped electrodes which form a matrixin the time display portion 51. The scanning electrode C5 and thescanning electrode C6 are connected, in series, to a plurality ofcircular and square electrodes which constitute two pair of mark displayportions 52 and display in multiple colors.

In the drawing, the scanning electrodes C1 to C6 are extended to theleft side of the display screen for easy explanation. Practically, thescanning electrodes C1 to C6 are generally connected with the secondsubstrate 2 by a conductive paste or anisotropic conductive beads.

As shown in FIG. 17, the second electrodes 4 of the liquid crystal cell12 consist of ten data electrodes D1 to D10. Each of the data electrodesD1 to D10 is connected to both the vertical bar-shaped electrode,forming a matrix in the letter display portion 51, and the circular orsquare electrode, forming the mark display portions 52, of which thecapacities of interconnections are approximately the same to improveevenness of display.

A method for driving the liquid crystal display device 18 will bedescribed below with references to the driving signals shown in FIG. 18and FIG. 19.

FIG. 18 shows signals supplied to the scanning electrodes C1 to C6 shownin FIG. 16. FIG. 19 shows signals supplied to the data electrodes D1 toD5 of the data electrodes shown in FIG. 17, and combination waveformssupplied to the liquid crystal between the scanning electrode C5 for themark display portion 52 and the data electrodes.

In the second embodiment, the drive of the liquid crystal display device18 with the quadplex drive, a one-third bias and a drive voltage of 3Vis explained. When a normal scanning signal is supplied to a scanningelectrode, the combination waveform with a data signal supplied to adata electrode becomes Von=1.73V and Voff=1.0V as an effective value, sothat the letter display portion 51 displays green letters on a blackbackground. Other values of voltage described below are all effectivevalues.

As shown in FIG. 18, normal scanning signals are supplied to thescanning electrodes C1 to C4 for the letter display portion 51, but datasignals are supplied to the scanning electrodes C5 and C6 for the markdisplay portions 52. Here, the data signal of ONION/ONION is assigned tothe scanning electrode C5, and the data signal of OFF/OFF/OFF/OFF isassigned to the scanning electrode C6.

Accordingly, as shown in FIG. 19, five strengths of voltage, V4=2.0V,V3=1.73V, V2=1.41V, V1=1.0V and V0=0V, are applied as the combinationwaveform, due to the data signals received by the data electrodes D1 toD5, to pixels connected to the scanning electrode C5.

As shown in the top boxes in FIG. 19, an OFF/OFF/OFF/OFF data signal issupplied to the data electrode D1. Hence, the pixel of the letterdisplay portion 51 connected to the data electrode D1 has Voff=1.0V, sothat the pixel displays in a black color which is the same as that ofthe background color. However, the combination waveform with the signalfor the scanning electrode C5 has V4=2.0V, so that the circular pattern(pixel) 53 in the mark display portion 52 shown in FIG. 11 displays alight green color.

As shown in the second box in FIG. 19, an OFF/OFF/OFF/ON data signal issupplied to the data electrode D2. Hence, the combination waveform withthe signal for the scanning electrode C5 has V3=1.73V, so that thesquare pattern 54 in the mark display portion 52 shown in FIG. 11displays a green color.

In the third box in FIG. 19, an OFF/ON/OFF/ON data signal is supplied tothe data electrode D3. Hence, the combination waveform with the signalfor the scanning electrode C5 has V2=1.41V, so that the display color ofthe circular pattern 55 in the mark display portion 52, shown in FIG.11, is blue.

In the fourth box in FIG. 19, an ON/ON/ON/OFF data signal is supplied tothe data electrode D4. Hence, the combination waveform with the signalfor the scanning electrode CS has V1=1V, so that the display color ofthe square pattern 56 in the mark display portion 52, shown in FIG. 11,is black which is the same as that of the background color.

In the bottom box in FIG. 19, an ON/ON/ON/ON data signal is supplied tothe data electrode D5. Hence, the combination waveform with the signalfor the scanning electrode C5 has V0=0V, so that the display color ofthe circular pattern 57 in the mark display portion 52, shown in FIG.11, is black, similar to the square pattern 56, which is the same asthat of the background color.

As described hereinbefore, the birefringence color liquid crystaldisplay device 18 is driven using the typical monochrome liquid crystaldriving IC without a gray scale function, whereby the letter displayportion 51 is allowed to display green letters on a black background,and each pattern (pixel) in the mark display portions 52 is allowed todisplay in multiple colors such as black/blue/green/light green. Sincethe monochrome liquid crystal driving IC has a simple circuit, a smallsize and low power consumption compared with those of a color liquidcrystal driving IC, the use of monochrome liquid crystal driving IC ispreferable due to longer battery life in portable machines, a timepieceor the like.

The data signals are changed at intervals of from approximately 0.1seconds to one second and supplied to the data electrode, whereby thedisplay color of each pattern in the mark display portions 52 in turn ischanged at intervals of 0.1 seconds to one second, thus allowing acolorful and impressive display screen, resulting in the provision ofnovel portable machines for young people.

Modification of the Second Embodiment

In the liquid crystal display device of the second embodiment, thetransflective reflector 11 is used as a reflector, and the backlightunit 19 is installed , thereby allowing visibility of the display evenat night. However, a reflector may be used for only reflecting withoutemploying the backlight unit 19.

The liquid crystal display device of the embodiment uses the STN modeliquid crystal cell 12 having a Δnd value=1680 nm at a twist angle of240°, and the retardation film 13 having a retardation value of 1800 nm.However, a display color similar to that in the second embodiment can beobtained insofar as a Δnd value of the STN mode liquid crystal cell 12ranges from 1500 nm to 1800 nm, and the retardation film 13 has aretardation value from 50 nm to 200 nm larger than a Δnd value of theliquid crystal cell 12.

When a Δnd value of the liquid crystal cell 12 is smaller than 1500 nm,the amount of the change in an apparent Δnd value through theapplication of voltage decreases, thus colors of blue and green are noteasily displayed. On the other hand, when the Δnd value exceeds 1800 nm,variations in color occurs abruptly, and the amount of color-variationdue to inconsistencies and temperature unfavorably increases.Consequently, any Δnd value of less than 1500 nm and more than 1800 nmis undesirable.

Even in the use of any one of a TN mode liquid crystal cell, an STN modeliquid crystal cell having a twist angle of more than 180° and acombination of a retardation film and a STN mode liquid crystal cellhaving a twist angle of more than 180°, the birefringence color liquidcrystal display device similar to that described in the embodiment, butdiffering in the color tone therefrom, can be designed, thus providing acolorful watch.

The liquid crystal display device of the embodiment uses a uniaxialstretching film made of a polycarbonate film as the retardation film 13.However, the viewing angle characteristic can be further improved byemploying a biaxial retardation film having the relations of nx>nz>ny,where nx is the refractive index in the direction of a phase delay axis13 a of the retardation film, ny is the refractive index in the y-axisdirection orthogonal to the phase delay axis 13 a, and nz is therefractive index in the z-axis direction as the thickness direction.

An improved color display is allowed by employing, instead of theretardation film 13, a twisted retardation film which is coated andfixed with a liquid crystal polymer on a triacetyl cellulose (TAC) filmor a polyester (PET) film.

As a result of utilizing the liquid crystal cell 12, with Δnd=1680 nm ofthe embodiment, and the twisted retardation film, with a Δnd value=1650nm at a clockwise twist angle of 240°, in combination, a birefringencecolor liquid crystal display device capable of displaying information inbright colors on a black background is achieved, resulting in a watchwith a further colorful display.

When the birefringence color liquid crystal display device isconstructed of the STN mode liquid crystal cell 12 and the twistedretardation film, by using the STN mode liquid crystal cell 12 having aΔnd value ranging from 1500 nm to 1800 nm and the twisted retardationfilm having a Δnd value from 10 nm to 100 nm smaller than the Δnd valueof the liquid crystal cell 12, colors similar to those of the embodimentare obtained.

In the birefringence color liquid crystal display device, installing thetwisted retardation film, when a Δnd value of the liquid crystal cell 12is smaller than 1500 nm, the amount of the change in an apparent Δndvalue through the application of voltage decreases, thus colors of blueand green are not easily displayed. And the Δnd value that exceeds 1800nm is undesirable, because variations in color occurs vigorously andabruptly, and the amount of color-variation due to inconsistencies andtemperature increases.

The second embodiment describes the liquid crystal display device for awatch, but as a matter of course, the present invention is adaptable toa liquid crystal display device for a portable tape recorder, a cellularphone or the like.

The embodiment describes the first electrodes 3 as the scanningelectrodes and the second electrodes 4 as the data electrodes, butreversibly, the second electrodes 4 may operate as the scanningelectrodes and the first electrodes 3 may operate as the dataelectrodes. In this case, the scanning signals are assigned to thesecond electrodes 4 for the time display portion 51 and the data signalsare assigned to the second electrodes 4 for the mark display portions52.

In the embodiment, a simple shape, such as a circle and square, is usedin the mark display portion of the liquid crystal display device, but itmay be an elaborate graphic, a letter shape or a shape of an animal orvehicle etc.

The aforementioned embodiment describes about the 1/4 duty multiplexdrive as the driving method for the liquid crystal display device.However, preferably, if the number of duty N further increases, aneffective value of the combination waveform for the mark display portiontakes N+1, so that an optimum voltage for the liquid crystal displaydevice can be easily selected for the effective value.

The aforementioned embodiment explains the driving method for the liquidcrystal display device taking, as an example, the in-a-line reversedriving for reversing positive and negative poles within a frame so asto avoid the application of direct current to the liquid crystal cell,but the liquid crystal display device may be driven by employing ann-line reverse driving for reversing positive and negative poles every nline, or a frame reverse driving for reversing positive and negativepoles every frame.

Third Embodiment: FIGS. 20 to 23

A third embodiment according to the present invention will be describedbelow with references to FIG. 20 to FIG. 23. The same reference numeralswill be used to designate the same components as those described in thefirst and second embodiments and the description thereof will beomitted.

The liquid crystal display device of the third embodiment is a two-stageliquid crystal display device which includes a first liquid crystaldisplay device 61 and a second liquid crystal display device 63, asshown in FIG. 21.

As shown in FIG. 20, a display portion of the first liquid crystaldisplay device 61 consists of the letter display portion 41 fordisplaying a current time, alarm time or the like. A display portion ofthe second liquid crystal display device 63 composes a rectangularshutter portion 47 as indicated with the broken line in FIG. 20.

Since the second liquid crystal display portion 63 lies upon the firstliquid crystal display portion 61, a silver color is displayed to hidethe letter display portion 41 while the shutter portion 47 is closed.When the shutter portion 47 is opened, the letter display portion 41becomes visible.

While the shutter portion 47 is closed, the display assumes a mirrorstate completely, so that the watch or the portable machine looks likean accessory, resulting in the provision of fashionable and attractivewatch or portable machines.

The configuration of the two-stage liquid crystal display device of thethird embodiment will be explained with reference to FIG. 21 being asectional view thereof, and FIG. 22 and FIG. 23 which are plane viewseach showing a positional relation between a liquid crystal cell andpolarizing films.

In FIG. 21, the first liquid crystal display device 61 is composed of aTN mode first liquid crystal cell 60, comprising: the first substrate 1which is made of a glass plate with a thickness of 0.5 mm and on whichfirst electrodes 3, made of ITO, are mounted; the second substrate 2which is made of a glass plate with a thickness of 0.5 mm and on whichsecond electrodes 4, made of ITO, are mounted; the sealing member 5 foradhering between the first substrate 1 and the second substrate 2; andthe nematic liquid crystal 6 which is aligned at a twist angle of 90°,and which is sandwiched and filled in a gap between the first substrate1 and the second substrate 2.

The first polarizing film 9 and the transflective reflector 11 arearranged outside the first substrate 1 of the first liquid crystal cell60. The second polarizing film 8 lies outside the second substrate 2.

Since the transflective reflector 11 partly transmits light fromunderneath, the backlight unit 19 is provided in the watch so as todesign a translucent-type liquid crystal display device.

The second liquid crystal display device 63 is formed as a TN modesecond liquid crystal cell 62 by: a first substrate 71 which is made ofa glass plate with a thickness of 0.3 mm and on which a first electrode73, made of ITO, is mounted; a second substrate 72 which is made of aglass plate with a thickness of 0.3 mm and on which a second electrode74, made of ITO, is mounted; a sealing member 75 for adhering betweenthe first substrate 71 and the second substrate 72; and a nematic liquidcrystal 76 which is aligned at a twist angle of 90°, and which issandwiched and filled in a gap between the first substrate 71 and thesecond substrate 72.

Outside the first substrate 71 of the second liquid crystal cell 62, areflection-type polarizing film 65 is laid. Outside the second substrate72, a third polarizing film 64 is laid. The reflection-type polarizingfilm 65 is a film which is formed by laminating more than 100 layerseach formed with a materials dissimilar in refractive index, and whichhas the properties of transmitting a linearly polarized light in thedirection parallel to the transmission axis, but reflecting a linearlypolarized light in the direction orthogonal to the transmission axis. Inthe embodiment, D-BEF-A (trade name) made by 3M Co., Ltd. is used forthe film.

On the surfaces of the first electrodes 3 and the second electrodes 4 ofthe first liquid crystal cell 60, alignment layers (not shown) areformed respectively. As shown in FIG. 22, the first substrate 1undergoes a rubbing treatment downward to the right at a 45° angle withrespect to the horizontal axis H, whereby a lower molecular alignmentdirection 60 a of liquid crystal is disposed downward to the right at a45° angle. The second substrate 2 undergoes a rubbing treatment upwardto the right at a 45° angle, whereby an upper molecular alignmentdirection 60 b of liquid crystal is disposed upward in the right at a45° angle. The nematic liquid crystal has a viscosity of 20 cp. Aso-called “chiral” substance, which is an optical rotatory material, isadded to the nematic liquid crystal. The chiral substance is added suchthat the twisting pitch P is adjusted to approximately 100 μm, thusforming the TN mode first liquid crystal cell 60 twistedcounterclockwise at a 90° angle.

A difference Δn in birefringence of the nematic liquid crystal 6 used inthe first liquid crystal cell 60 is set to be 0.15 and a cell gap dwhich is a gap between the first substrate 1 and the second substrate 2is set to be 8 μm. Accordingly, the Δnd value of the first liquidcrystal cell 60 which is represented by the product of the difference Δnin the birefringence of the nematic liquid crystal 6 and the cell gap d,is 1200 nm.

Alignment layers (not shown) are also formed on the respective surfacesof the first electrode 73 and the second electrode 74 of the secondliquid crystal cell 62. As shown in FIG. 23, the first substrate 71undergoes a rubbing treatment downward in the right at a 45° angle withrespect to the horizontal axis H, whereby a lower molecular alignmentdirection 62 a of liquid crystal is disposed downward to the right at a45° angle. The second substrate 72 undergoes a rubbing treatment upwardto the right at a 45° angle, whereby an upper molecular alignmentdirection 62 b is disposed upward to the right at a 45° angle. Thenematic liquid crystal has a viscosity of 20 cp. A chiral substance,which is an optical rotatory material, is added to the nematic liquidcrystal. The chiral substance is added such that the twisting pitch P isadjusted to approximately 100 μm, thus forming the TN mode second liquidcrystal cell 62 twisted counterclockwise at 90° angle.

A difference Δn in birefringence of the nematic liquid crystal 76 usedin the second liquid crystal cell 62 is set to be 0.15 and a cell gap dwhich is a gap between the first substrate 71 and the second substrate72 is set to be 8 μm. Accordingly, a Δnd value of the second liquidcrystal cell 62 which is represented by the product of the difference Δnin the birefringence of the nematic liquid crystal 76 and the cell gapd, is also 1200 nm.

As shown in FIG. 22, the absorption axis 8 a of the second polarizingfilm 8, incorporated in the first liquid crystal display device 61, isdirected upward to the right at a 45° angle equivalent to that in theupper molecular alignment direction 60 b of the first liquid crystalcell 60. The absorption axis 9 a of the first polarizing film isdirected downward to the right at a 45° angle equivalent to that in thelower molecular alignment direction 60 a of the first liquid crystalcell 60. Consequently, the pair of upper and lower polarizing films 8and 9 forms an intersecting angle of 90°.

As shown in FIG. 23, an absorption axis 64 a of the third polarizingfilm 64 incorporated in the second liquid crystal display device 62, isdirected upward to the right at a 45° angle equivalent to that in theupper molecular alignment direction 62 b of the second liquid crystalcell 62. A transmission axis 65 a of the reflection-type polarizing film65 is directed downward to the right at a 45° angle equivalent to thatin the lower molecular alignment direction 62 a of the second liquidcrystal cell 62.

As for the above-described two-stage liquid crystal display device ofthe third embodiment, where a voltage is not applied to the secondliquid crystal cell 62, after a linearly polarized light passes throughthe third polarizing film 64 to be transmitted from a directionorthogonal to the absorption axis 64 a, it is rotated at a 90° angle bythe second liquid crystal cell 62 to bear towards the reflection axisorthogonal to the transmission axis 65 a of the reflection-typepolarizing film 65, hence all the incident light is reflected and thedisplay results in a silver mirror display.

When a voltage is applied across the first electrode 73 and the secondelectrode 74 of the second liquid crystal cell 62, molecules of thenematic liquid crystal 76 rise and the optical rotatory character of thesecond liquid crystal cell 62 is lost. Therefore, the linearly polarizedlight after passing through the third polarizing film 64 and beingincident from a direction orthogonal to the absorption axis 64 a,advances in a direction parallel to the transmission axis 65 a of thereflection-type polarizing film 65, so that the incident light is passedthrough the second liquid crystal display device 63, and the shutterportion 47 shown in FIG. 20 is opened.

When opening the shutter portion 47, a transmission axis orthogonal tothe absorption axis 8 a of the second polarizing film in the firstliquid crystal display device 61, is parallel to the transmission axis65 a of the reflection-type polarizing film 65 in the second liquidcrystal display device 63, so that the linearly polarized light passedthrough the second liquid crystal display device 63, is incident ontothe first liquid crystal display device 61.

Where a voltage is not applied to the first liquid crystal cell 60, thelinearly polarized light advancing from the second polarizing film 8 isrotated at 90° angle and reaches in the transmission-axis directionorthogonal to the absorption axis 9 a of the first polarizing film 9, sothat the incident light passes through the first polarizing film 9.Thereafter, the incident light is reflected by the transflectivereflector 11, and then again returns to pass through the first liquidcrystal display device 61 and the second liquid crystal display device63, to be emitted to the visible side, resulting in the display in awhite color.

When a voltage is applied across the first electrodes 3 and the secondelectrodes 4 of the first liquid crystal cell 60, molecules of thenematic liquid crystal 6 rise and the optical rotatory character of thefirst liquid crystal cell 60 is lost. Therefore, the linearly polarizedlight passed through the second polarizing film 8 from a directionorthogonal to the absorption axis 8 a, advances in a direction parallelto the absorption axis 9 a of the first polarizing film 9, thus all theincident light is absorbed and the first liquid crystal display devicedisplays in a black color.

A method for driving the two-stage liquid crystal display device of thethird embodiment will now be explained. The driving signals used in themethod are the same as those used in the first embodiment shown in FIG.8 and FIG. 9. The first electrodes 3 in the first liquid crystal cell 60consist of the scanning electrodes C1 to C3 as shown in FIG. 6, and thescanning signals as shown in FIG. 8 are supplied thereto. The secondelectrodes 4 consist of the data electrodes D1 to D20 as shown in FIG.7, and the data signals as shown in FIG. 9 are supplied thereto so as toperform the display of time or the like.

The first electrode 73 in the second liquid crystal cell 62 consists ofa scanning electrode, and the data signal for C4 shown in FIG. 8 isassigned thereto. The second electrode 74 consists of a data electrode,and receives the data signal for D1 shown in FIG. 9, whereby thecombination waveform as shown in FIG. 9 is applied across the firstelectrode 73 and the second electrode 74, hence a voltage of 3V can beapplied as an effective value.

As shown in FIG. 10, to the first liquid crystal cell 60 only Von=2.12Vis applied, but to the second liquid crystal cell 62 a voltage ofV3=3.0V can be applied. Accordingly, the second liquid crystal cell 62assumes a completely opening state, resulting in a shuttercharacteristic with a shine and the improved viewing anglecharacteristic.

By supplying the data signal D5 or D9, as shown in FIG. 9, to the secondelectrode 74 of the second liquid crystal cell 62, the second liquidcrystal display device 63 is allowed to take a half-open state,alternatively, to be controlled to gradually display time when openingor cover the time when closing.

Through driving the two-stage liquid crystal display device with atypical monochrome liquid crystal driving IC without a gray scalefunction, the effective voltage applied to the second liquid crystaldisplay device 63 is allowed to be set at a value larger than that ofthe effective voltage applied to the first liquid crystal displaydevice, whereby the shutter portion can assume a full open state toallow a bright display, resulting in the provision of novel portablemachines, a watch or the like, for young people in which letters emergefrom a metallic shutter.

Modification of the Third Embodiment

In the third embodiment, the transflective reflector 11 is used as areflector and the backlight unit 19 is provided for visibility of thedisplay at night. However, a reflector may be used as a dedicated typefor reflection, not to employ the backlight unit 19.

While the third polarizing film 64 and the reflection-type polarizingfilm 65 are provided in the second liquid crystal display device 63, thesecond liquid crystal display device 63 may consist of only the thirdpolarizing film 64 replacing the reflection-type polarizing film 65.Alternatively, the reflection-type polarizing film 65 may be replacedwith a typical absorption type polarizing film, in which the displayassumes not a mirror state, but a black or white background.

The TN liquid crystal cell having a twist angle of 90° is used for thefirst liquid crystal cell 60 and the second liquid crystal cell 62 inthe embodiment. However, an STN liquid crystal cell having a twist anglein range from 180° to 270° can be used, or a liquid crystal displaydevice incorporated with an STN liquid crystal cell having a retardationfilm or a twisted retardation film can be used.

In the embodiment, the second liquid crystal display device 63 isprovided with only one shutter portion 47, but a plurality of shutterportions can be provided as a matter of course.

The embodiment has described the two-stage liquid crystal display deviceincluding the first liquid crystal display device 61 and the secondliquid crystal display device 63. However, even a conventional liquidcrystal display device can display with emphasis on contrast in a markportion or an icon portion or can perform a half tone display insofar asthe driving method of the liquid crystal display device according to thepresent invention is applied to the operation of the conventional liquidcrystal display device.

Industrial Applicability

As is clear from the aforementioned description, a liquid crystaldisplay device according to the present invention comprises abirefringence color liquid crystal display device of which a liquidcrystal display portion consists of a letter display portion and a markdisplay portion, the mark display portion displaying in multiple colorsso as to provide a colorful and fashionable display.

A multicolor display is achieved by driving the birefringence colorliquid crystal display device with a typical monochrome liquid crystaldriving IC without a gray scale function, thus providing portablemachines capable of displaying in multiple colors with a low cost and alow power consumption.

A timepiece, comprising a two-stage liquid crystal display device inwhich a second liquid crystal display device is mounted on a firstliquid crystal display device as explained in the third embodiment, hasa high contrast on the second liquid crystal display device and isallowed to perform a half tone display, thus providing fashionable andattractive portable machines having brightness and a brightnessadjusting function.

What is claimed is:
 1. A liquid crystal display device, consisting of aliquid crystal cell in which nematic liquid crystal is sandwiched andfilled in a gap between a transparent first substrate having firstelectrodes and a transparent second substrate having second electrodesand a liquid crystal driving circuit which outputs scanning signals anddata signals for driving said liquid crystal display cell, wherein adisplay portion has a letter display portion and a mark display portion,and said liquid crystal driving circuit supplies scanning signals tosaid first electrodes while supplying data signals to said secondelectrodes in said letter display portion, and data signals to both saidfirst electrodes and second electrodes in said mark display portion. 2.The liquid crystal display device according to claim 1, furthercomprising a reflector which is a transflective reflector is arranged onthe outside of said liquid crystal cell, and a backlight unit arrangedon the opposite side of said transflective reflector from said liquidcrystal cell to illuminate said liquid crystal cell through saidtransflective reflector.
 3. The liquid crystal display device accordingto claim 1, further comprising a pair of polarizing films arranged onand under the liquid crystal cell, and a retardation film arrangedbetween said liquid crystal cell and said polarizing film positioned onthe visible side.
 4. The liquid crystal display device according toclaim 2, further comprising a pair of polarizing films arranged on andunder the liquid crystal cell, and a retardation film arranged betweensaid liquid crystal cell and said polarizing film positioned on thevisible side.
 5. The liquid crystal display device according to claim 1,further comprising a pair of polarizing films arranged on and under theliquid crystal cell, and a twisted retardation film arranged betweensaid liquid crystal cell and said polarizing film positioned on thevisible side.
 6. The liquid crystal display device according to claim 2,further comprising a pair of polarizing films arranged on and under theliquid crystal cell, and a twisted retardation film arranged betweensaid liquid crystal cell and said polarizing film positioned on thevisible side.
 7. The liquid crystal display device according to claim 1,wherein said liquid crystal cell is an STN liquid crystal cell in whichsaid nematic liquid crystal is aligned at a twist angle in the rangefrom 180 degrees to 270 degrees, and a Δnd value which is the product ofa value Δn in the birefringence of the liquid crystal and a gap d of theliquid crystal cell, ranges from 1300 nm to 1600 nm.
 8. The liquidcrystal display device according to claim 2, wherein said liquid crystalcell is an STN liquid crystal cell in which said nematic liquid crystalis aligned at a twist angle in the range from 180 degrees to 270degrees, and a Δnd value which is the product of a value Δn in thebirefringence of the liquid crystal and a gap d of the liquid crystalcell, ranges from 1300 nm to 1600 nm.
 9. The liquid crystal displaydevice according to claim 3, wherein said liquid crystal cell is an STNliquid crystal cell in which said nematic liquid crystal is aligned at atwist angle in the range from 180 degrees to 270 degrees, and a Δndvalue which is the product of a value Δn in the birefringence of theliquid crystal and a gap d of the liquid crystal cell, ranges from 1500nm to 1800 nm, and a retardation value of said retardation film rangesfrom 1600 nm to 1900 nm.
 10. The liquid crystal display device accordingto claim 4, wherein said liquid crystal cell is an STN liquid crystalcell in which said nematic liquid crystal is aligned at a twist angle inthe range from 180 degrees to 270 degrees, and a Δnd value which is theproduct of a value Δn in the birefringence of the liquid crystal and agap d of the liquid crystal cell, ranges from 1500 nm to 1800 nm, and aretardation value of said retardation film ranges from 1600 nm to 1900nm.
 11. The liquid crystal display device according to claim 3, whereinsaid retardation film is a retardation film forming relations ofnx>nz>ny, where nx is the refractive index of a phase delay axis, ny isthe refractive index in a direction orthogonal to the phase delay axis,and nz is the refractive index in a thickness direction.
 12. The liquidcrystal display device according to claim 4, wherein said retardationfilm is a retardation film forming relations of nx>nz>ny, where nx isthe refractive index of a phase delay axis, ny is the refractive indexin a direction orthogonal to the phase delay axis, and nz is therefractive index in a thickness direction.
 13. The liquid crystaldisplay device according to claim 5, wherein said liquid crystal cell isan STN liquid crystal cell in which said nematic liquid crystal isaligned at a twist angle in the range from 180 degrees to 270 degrees,and a Δnd value which is the product of a value Δn in the birefringenceof the liquid crystal and a gap d of the liquid crystal cell, rangesfrom 1500 nm to 1800 nm, and a Δnd value of said twisted retardationfilm ranges from 1400 nm to 1800 nm.
 14. The liquid crystal displaydevice according to claim 6, wherein said liquid crystal cell is an STNliquid crystal cell in which said nematic liquid crystal is aligned at atwist angle in the range from 180 degrees to 270 degrees, and a Δndvalue which is the product of a value Δn in the birefringence of theliquid crystal and a gap d of the liquid crystal cell, ranges from 1500nm to 1800 nm, and a Δnd value of said twisted retardation film rangesfrom 1400 nm to 1800 nm.
 15. A liquid crystal display device,comprising: a first liquid crystal cell in which nematic liquid crystalis sandwiched and filled in a gap between a transparent first substratehaving first electrodes and a transparent second substrate having secondelectrodes; a second liquid crystal cell in which nematic liquid crystalis sandwiched and filled in a gap between a transparent first substratehaving a first electrode and a transparent second substrate having asecond electrode, arranged on a visible side to the first liquid crystalcell; and a liquid crystal driving circuit which outputs scanningsignals and data signals for driving said first and second liquidcrystal display cells, wherein a liquid crystal driving circuit is acircuit for supplying said scanning signals to said first electrodes ofsaid first liquid crystal cell, said data signals to said secondelectrodes of said first liquid crystal cell, and said data signals toboth said first electrode and said second electrode of said secondcrystal liquid cell.
 16. A liquid crystal display device comprising: afirst liquid crystal display device consisting of a first liquid crystalcell in which nematic liquid crystal is sandwiched and filled in a gapbetween a transparent first substrate having first electrodes and atransparent second substrate having second electrodes, a pair ofpolarizing films respectively arranged on and under the first liquidcrystal cell, and a reflector arranged on a face of one of thepolarizing films, the face being on the opposite side to said liquidcrystal cell; a second liquid crystal display device arranged on thevisible side of said first liquid crystal display device, and consistingof a second liquid crystal cell in which nematic liquid crystal issandwiched and filled in a gap between a transparent first substratehaving first electrode and a transparent second substrate having asecond electrode, a third polarizing film arranged on a face of thesecond liquid crystal cell on the visible side, and a reflection-typepolarizing film arranged on the opposite side of said second liquidcrystal cell from the visible side; and a liquid crystal driving circuitfor driving said first and second liquid crystal cells to supplyscanning signals to said first electrodes of said first liquid crystalcell, data signals to said second electrodes of said first liquidcrystal cell, and data signals to said first electrode and said secondelectrode of said second crystal liquid cell.
 17. A method for driving aliquid crystal display device, comprising a liquid crystal cell in whichnematic liquid crystal is sandwiched and filled in a gap between atransparent first substrate having first electrodes and a transparentsecond substrate having second electrodes, a liquid crystal drivingcircuit which outputs scanning signals and data signals for driving saidcrystal display cell, wherein a display portion of said liquid crystaldisplay device has a letter display portion and a mark display portion,said method comprising steps of: supplying scanning signals to saidfirst electrodes while supplying data signals to said second electrodesin said mark display portion for displaying a single color; andsupplying data signals to both said first electrode and second electrodein said mark display portion for displaying in a plurality of colors.18. A method for driving a liquid crystal display device, comprising afirst liquid crystal cell in which nematic liquid crystal is sandwichedand filled in a gap between a transparent first substrate having firstelectrodes and a transparent second substrate having second electrodes,;a second liquid crystal cell in which nematic liquid crystal issandwiched and filled in a gap between a transparent first substratehaving a first electrode and a transparent second substrate having asecond electrode, arranged on a visible side of the first liquidcrystal, and a liquid crystal driving circuit which outputs scanningsignals and data signals for driving said first and second crystaldisplay cells, said method comprising steps of: supplying scanningsignals to said first electrodes of said first liquid crystal cell whilesupplying data signals to said second electrodes thereof; for displayinga single color; and supplying data signals to both said first electrodeand said second electrode of said second liquid crystal cell fordisplaying in a plurality of colors.
 19. The liquid crystal displaydevice according to claim 1, wherein said letter display portion is adisplay portion displaying in a single color, and said mark displayportion is a display portion displaying in a plurality of colors. 20.The liquid crystal display device according to claim 2, wherein saidletter display portion is a display portion displaying in a singlecolor, and said mark display portion is a display portion displaying ina plurality of colors.